For example, Greg Cochran likes togoonabout how major ancestry groups often differ in crude brain morphology, and how these differences probably explain a significant chunk (> 20%) of bio-ancestry related differences in CA. I doubt it. But if he agrees to specify the analytic strategy, I will try to get the data and run the analyses.

I did look through the PING survey (age 3-21, N ~ 1,500) – which might not be very informative owing to the age structure. Going by this, Greg seems to be more or less correct about some of the endo differences and probably about their origins. As an example, Figure 1 & 2 show the B/W diffs for intracranial and total brain volume by age. (AAs are picked out for illustration since they are the largest non-White ethnic group, showing the biggest deviation from Whites.) And Figure 3 shows the relation between brain volume and ancestry in the self-identified AA group; the results were basically the same for intracranial volume, etc. — and so not shown.

Yet, as seen in Table 1 & 2, CA was more or less uncorrelated with these particular endophenotypes (r = 0.07-0.08); unsurprisingly, CA explained virtually no endo differences, and vice versa. Yet, CA was strongly (negatively) associated with both African and Amerindian ancestry – and also, though to a lesser degree, with Oceanian.

Perhaps there is a more sound way to run the numbers? Or a better way to take into account age? Dunno, it’s not my position to defend.